The DC to DC converter of this invention is an improvement over our copending patent application mentioned above in that the same ripple free currents in both input and output connections are achieved using but three coupled inductor windings and associated inductance tuning in place of the four coupled inductors used in our copending patent application.
Our copending patent application was developed from the theories expressed in our paper entitled "Practical Design Considerations For A Multi-Output Optimum Topology Converter" by Gordon E. Bloom and Altan Eris, published in IEEE International Power Specialists Conference (IPSC) presented in San Diego, California, June, 1979; and republication in European Power Convention '79 presented in Munich, West Germany, Sept. 17-21, 1979.
In turn, the apparatus of our copending patent application, from which this invention is a continuation-in-part, is an improvement over the circuits conceived by Slobodan Cuk, et al., as described, for example, in Electronic Design News, May 20, 1979, on pages 54, et. seq.
A still further description of the prior art may be found in "Coupled-Inductor and Other Extensions of a New Optimum Topology Switching DC-to-DC Converter" by Slobodan Cuk and R.D. Middlebrook in IAS 77 Annual, pages 1110, et seq.
The authors of those papers refer to U.S. Pat. application Ser. No. 837,532, filed Sept. 26, 1977, the subject matter of which is unknown to the inventors of this invention. That patent application issued Jan. 15, 1981 as U.S. Pat. No. 4,184,197.
Cuk, et al., have described a circuit which either produces a zero rippled output current or a zero ripple input current, but not both. See "Switching DC-to-DC Converter with Zero Input or Output Current Ripple" by Slobodan Cuk, Proceedings of IEEE Industry Applications Society Annual Meeting, Toronto, Canada, Oct. 1-5, 1978.
The Cuk apparatus utilizes a pair of tightly coupled windings wherein the inductances may be adjusted either to cause the output current to be ripple free or to cause the input current to be ripple free. Typically the Cuk apparatus has the two closely coupled windings in series connection with an energy transfer capacitor between them. The two sides of the capacitor are alternately grounded, and the careful adjustment of inductance values and coupling coefficient causes the current through the load or the input current to be substantially ripple free.
This invention, as described herein, is an improvement over our copending patent application which, in turn, was an improvement over the Cuk apparatus described above. The copending patent application of which this is a continuation replaced the single series capacitor of Cuk with two series capacitors and connected the junction between the capacitors through two parallel inductors to ground. Through this arrangement, it was possible to provide both input and output terminals with substantially ripple free currents. The Cuk apparatus was capable of providing a ripple free current only at the input or output terminals but not both.
The present invention carries our copending patent application one step further. That is, the present invention retains the ability of obtaining both input and output currents that are substantially ripple free but accomplishes this same result with fewer components. The present invention retains the serially-connected capacitors in place of the single Cuk capacitor. However, in place of the two parallel inductors connected to ground taught by our copending application, the present invention utilizes but a single inductor connected to ground.
Therefore, it is an object of the present invention to accomplish the same function as the prior art with fewer components.
Another object of the present invention is to provide an optimum topology converter having a no ripple current in either of the input and output circuits.